Curiosity Mars Hand Lens Imager (MAHLI) photo produced on Sol 1984, March 6, 2018.
Credit: NASA/JPL-Caltech/MSSS

Just how hard is a rock and any way to tell ahead of drilling?

That’s the question raised by Roger Wiens, a geochemist at Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico.

Curiosity Mastcam Right image taken on Sol 1983, March 5, 2018.
Credit: NASA/JPL-Caltech/MSSS

“Last week when the first Vera Rubin Ridge drill-hole attempts turned out to be too shallow at ‘Lake Orcadie’ discussion in the team turned to the question of: “How hard is that rock? Is there a way to know before starting the drill hole how hard the rock will be, so we can anticipate whether Curiosity’s new drill technique will be successful?”

Curiosity Mastcam Left photo taken on Sol 1983, March 5, 2018.
Credit: NASA/JPL-Caltech/MSSS

Several indicators

Wiens reports that the rover team has several indicators of rock hardness:

a) retention of natural features such as craters,

b) the imprints of wheel marks on the rocks, when we see them,

c) scratch marks from the Dust Removal Tool (DRT) brush, and

d) laser pits from the rover’s Chemistry and Camera (ChemCam) instrument.

This turns out to be a lot of data, especially from ChemCam and the robot’s Mars Hand Lens Imager (MAHLI).

Mineral hardness scales

“However, no one has yet made a quantitative study of rock hardness vs. apparent laser pit depth or brush scratches,” Wiens adds. “The problem is that other factors can affect how deep the pit or scratches look in our images, especially including lighting angle and rock texture and color, but also, for the laser, the distance from the rover and the focus quality. Even so, a study to determine apparent laser pit depth or scratch depth vs. hardness may be useful.”

The classic Mohs mineral hardness scale, Wiens points out, was developed over 200 years ago, based on ten readily available minerals ranging from talc (hardness of 1) to diamond (hardness of 10).

Curiosity Front Hazcam Right B image acquired on Sol 1984, March 6, 2018.
Credit: NASA/JPL-Caltech

“It is still used because of its simplicity…you can buy a kit with each of the representative minerals and try using them to scratch the mineral that you want to test. However, for quantitative measurements, most studies use the Vickers scale, which was defined 100 years ago and is reported in kilogram per square millimeter. It is traditionally measured by the size of the indentation left from a diamond tip with a given force applied,” Wiens says.

Back to driving

Meanwhile, back on Mars, Curiosity is now performing Sol 1985 tasks.

The robot is slated to drive away from it current hard-rock location, with the first drive since Sol 1962, planned to go backwards for almost 100 feet (30 meters) in a northeasterly direction.

Curiosity’s Chemistry and Camera (ChemCam) Remote Micro-Imager took this photo of meteorite, “Ben Nevis_2” – a small iron clast with four bright glints, which are sunlight reflections off the metal made bare by previous ChemCam laser shots. Image taken on March 3, 2018, Sol 1981.
Credit: NASA/JPL-Caltech/LANL

Meteorite observations

“Prior to leaving this site, ChemCam and Mastcam will make one more observation each of a meteorite, “Ben Nevis_2” – a small iron clast with four bright glints, which are sunlight reflections off the metal made bare by previous ChemCam laser shots,” Wiens reports.

Also on the plan, Curiosity’s Mastcam will make crater rim extinction and basic tau (atmospheric visibility) observations. After the drive Mastcam, Hazcam, and Navcam will document the new rover surroundings.

Mt. Sharp mosaic

Navcam will take a zenith movie and a 360 degree observation. Mastcam will also take a clast survey image, and ChemCam will take a remote micro-imager (RMI) mosaic of the Yardang portion of Mt. Sharp.

ChemCam Remote Micro-Imager photo taken on Sol 1984, March 6, 2018.
Credit: NASA/JPL-Caltech/LANL

Wiens says that use of and will use Autonomous Exploration for Gathering Increased Science (AEGIS) software to select an outcrop target near the rover for chemical analysis.

Lastly, the rover’s Dynamic Albedo of Neutrons (DAN), Mars Descent Imager (MARDI), Radiation Assessment Detector (RAD), and Rover Environmental Monitoring Station (REMS) will also take data.

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